1. Field of the Invention
The present invention relates to a machine tool having an onboard measuring device.
2. Description of the Related Art
In an ultra precision machining, in order to achieve an accuracy of form of nano unit, a compensation machining by an onboard measurement is essential. In such onboard measurement, a machining object is not detached, as a result, it is possible to avoid occurrence of problems such as a repeatability in setting which is generated in a case where a machining object is detached and a thermal displacement of the machining object and the machine that is generated on the basis of a heat transmission from an operator's body at a time when the operator detaches or attaches the machining object. However, a conventional current onboard measuring system includes a portion to be manually carried out by a human operator when carrying out an onboard measurement, so it is necessary to remove such a portion from the onboard measuring system as much as possible so as to minimize an influence of the thermal displacement.
Further, in recent years, a demand for a high precision metal mold has been increased, and it comes to a matter of concern how production efficiency is raised. Accordingly, it is very important to shorten a cycle time for measuring and compensating as much as possible.
As a prior art onboard measuring system, for example, in Japanese Patent Application Laid-Open No. 2010-105063, there is disclosed a technique in which a measuring device is mounted on a machine tool, aiming at a high precision of a machining object and suppression of a thermal displacement (a temperature drift).
In the technique mentioned above, it is possible to do away with an attachment and detachment operation of the machining object, and avoid a direct contact of a worker with the machining object. However, a washing of the machining object during or after the machining or a positioning for a measuring work is performed according to a worker's judgment.
Accordingly, it is necessary to open a cover of a machine and perform a position check by a worker, and a temperature drift which is generated by an ambient air transmitted at that time will prevent a manufacturing of the metal mold having a high precision. Further, as a worker' judgment is required, it is necessary to temporarily interrupt the work every time machining, cleaning or measuring work is performed, so it is difficult to shorten a machining time which is important factor in a mass production of high precision metal molds. Further, the measurement precision and the machining time are widely changed dependent upon each worker's knowledge and a skill concerning an operation of an onboard measuring system, so it is difficult to stably produce metal molds each having a high accuracy of form.